When VW designed your engine, they picked the inside diameter of the bearings, and the outside diameter of the crankshaft journals that work with a 30 wt oil. Larger clearances are required when you build an engine to use that 60wt tar. Since it's pretty hard to increase the ID of the bearings, and much easier to grind the journals smaller, it's the crank that will be modified. Do you know if your engine builder ground your crank's journals smaller than VW's spec?
If your crank journals are ground to VW's spec, your engine builder is wrong.

even on days in the 90° I get 60#s of oil pressure when running off idle.

This is bad.
You know the pressure reading is in the cct between the pump and the bearings. When you get such a high reading, it tells me the oil is unable to get into the bearings. When that happens, it "backs up" causing the high readings.
If you had lower pressure, more oil would be passing through the bearings. That's a good thing, right?
The pressure relief valve dumps all oil pressure in excess of 42psi. When your engine produces pressure that high, it puts a ton of heat into the oil as it squirts out of the relief.
I bet you're using 20W-50?

Bruce, that is not an "at cold idle" pressure but warm oil pressure at normal (for the dunes) driving speeds; that is what "off idle" means. I have had many, many cars in the roughly 50 years of driving and have built many engines both stock and modified. I would agree with you that 60#s at idle is bad especially with a "cold" engine but my engine does run the 10#s of pressure for every 1000 RPMs and I do keep the RPMs even when climbing 100' dunes at under 5K. The additional deep sump also keeps oil starvation away (I lost one engine when oil pressure was lost when exiting the dunes on a very steep face) when working up, down, or when "facing" (driving across the face) a dune.

This engine is at least 10 years old but the run time on it isn't that great. When I built this one I was specific to what I wanted/needed plus the other limitations I also wanted so the cam is a high lift, short duration RV style engine with the RPM limitation of about 5500 and the oiling is full flow. When I got the case back from the machinist they noticed that they forgot to do the "sand seal" so I watch things a bit more than normal.

There are still several long dunes I want to "face" and maybe I will but then... maybe I won't make it that long. I've tried several of them but it seems like people don't look but will change up a dune right in front of someone else.

When VW designed your engine, they picked the inside diameter of the bearings, and the outside diameter of the crankshaft journals that work with a 30 wt oil. Larger clearances are required when you build an engine to use that 60wt tar. Since it's pretty hard to increase the ID of the bearings, and much easier to grind the journals smaller, it's the crank that will be modified. Do you know if your engine builder ground your crank's journals smaller than VW's spec?
If your crank journals are ground to VW's spec, your engine builder is wrong.

Thanks for your advice Bruce. I appreciate it.

I talked to all the local guys and they're all using the same oil as I am. So I ended up throwing the same spec oil back in. As to my engine builder, he is the son of a VW trained factory mechanic. He and his father opened their shop in the early 60s and fixed VW and porsche. My motor was one of the last he built before retiring last year. Ie. 55 years of VW specialist work. He's built more ACVW motors (street, race, offroad, drag, etc) than I've had hot dinners. So I'll take his tip on oil spec.

I'm not adverse to trying something thinner in the future, but not 5w30.

Either way, there will probably be more oil flowing between parts and actually cooling as it does so. I too was concerned and even a little skeptical when I first put my ACVW on the road. I went with 10/40 or a 15/40 and am now down to a 5/30 or a 10/30 and I have the same pressures and temps, possibly cooler on longer runs since the oil isn't bypassing the cooler anymore.